Disclosed is an electrical writable media having an islanded surface structure suitable for avoiding tribocharging. The electrical writable media may be a visual display or an electric paper. The islanded surface structure of the electrical media is operatively constructed to permit writing, erasing and no alteration of an image by using a stylus.
Various types of electric writable media, commonly known as electric paper, exist in the prior art. One example of electric paper includes a polymer substrate and bichromal anisotropic particles, such as balls or cylinders that are in suspension with an enabling fluid and are one color, such as white, on one side and a different color, such as black, on the other. Examples of such electric paper are described in U.S. Pat. No. 5,723,204 to Stefik and U.S. Pat. No. 5,604,027 to Sheridon, each of which is incorporated herein by reference in its entirety. Under the influence of an electric field, the particles rotate so that either the white side or the black side is exposed.
Another type of electric writable media is known as an electronic ink display, such as the one described in U.S. Pat. No. 6,518,949 to Drzaic, which is incorporated herein by reference. An electronic ink display includes at least one capsule filled with a plurality of particles, made of a material such as titania, and a dyed suspending fluid. When a direct-current electric field of an appropriate polarity is applied across the capsule, the particles move to a viewed surface of the display and scatter light. When the applied electric field is reversed, the particles move to the rear surface of the display and the viewed surface of the display then appears dark.
Yet another type of electric writable media, also described in U.S. Pat. No. 6,518,949 to Drzaic, includes a first set of particles and a second set of particles in a capsule. The first set of particles and the second set of particles have contrasting optical properties, such as contrasting colors, and can have, for example, differing electrophoretic properties. The capsule also contains a substantially clear fluid. The capsule has electrodes disposed adjacent to it connected to a voltage source, which may provide an alternating-current field or a direct-current field to the capsule. Upon application of an electric field across the electrodes, the first set of particles moves toward a first electrode, while the second set of particles moves toward a second electrode. If the electric field is reversed, the first set of particles moves toward the second electrode and the second set of particles moves toward the first electrode. Other examples of writable media include liquid crystal, non-encapsulated electrophoretic displays and other displays.
It has been well proven that electrostatic writing can be done on an erasable electric writable medium by swiping an array of electrodes across the surface with a printer-like motion, depositing charge on the surface in an image wise fashion. The charge, once deposited, places a voltage across the medium and causes it to change its electro-optic condition, for example, by rotating or twisting anisotropic particles, such as bichromal balls, or otherwise affecting a medium.
In one electrostatic display, there are used islanded structures of isolated conductive material on the top surface of the electric writable medium with associated display elements, such as rotatable balls having different colored surfaces. Such an islanded electric display is described in U.S. Pat. No. 6,222,513 to Howard et al. In such embodiment, the islands of conductive material act as a conducting surface for charge deposition that does not tribocharge with the writing array of electrodes and distributes the charge across each pixel in a relatively uniform manner.
There has recently been an effort to write on such islanded media with a single point stylus, much like a pen, which deposits charge on the surface causing the balls to rotate in a manner such that the desired color is displayed to the viewer. Attempts to perform stylus writing on electric writable media have generally focused on trying to perform one or more of three functions with the stylus: (1) writing on the electric writable media by applying a voltage with the stylus that rotates the affected rotatable elements or otherwise changes the affected portion of the medium from a background level, such as white, to a written level, such as black; (2) erasing the electric writable media by applying a voltage with the stylus that rotates the rotatable elements from a written level to a background level; and (3) moving the stylus on the electric writable media without affecting the disposition of the rotatable elements, thus enabling mouse-like action of the stylus. Unfortunately, the ability to achieve the functions of writing, erasing, and moving the stylus, as well as preventing the electric writable medium from “smudging” due to accidental contact with a stylus user's hand, has been difficult to achieve because of tribocharging caused by the motion of the stylus and/or the user's hand.
FIG. 1 depicts a cross-sectional view of an prior art electric writable medium 100. Electric writable medium 100 includes a conventional islanded structure of conductive material 102, 102′ and a cross-sectional view of a stylus 104 having a tip 108 with a radius of curvature R. Electric writable medium 100 is constructed of isolated conductive islands 102, 102′ placed on top of an insulating material 106 that are separated by a distance S. The thickness of isolated conductive islands 102, 102′, indicated by reference character H, is typically designed to be very thin. As a result, when the stylus tip 108 traces across the surface of the electric writable medium 100, it contacts both the conductive islanded material 102, 102′ and the insulating material 106, thereby rendering the air gap between the stylus tip 108 and insulating material 106 to zero. As a result, significant tribocharging of the electric writable medium 100 occurs as charges are stripped from the surfaces of the stylus 104 and the insulating material 106 and deposited on the surface of the conductive islands 102, 102′. This undesired charge transfer dominates the writing impact and inhibits the switching of the anisotropic particles in the electric writable medium 100. Moreover, if a user's hand rubs across the surface, the hand's motion can also produce a tribocharge that causes an undesirable smudge across the background.
Therefore, a need exists for an electric writable medium that permits stylus writing, erasing and/or moving without significant tribocharging.
Furthermore, a need exists for methods of writing on, erasing from and moving around, an electric writable media using a stylus.